Joint contribution of adaptation and neuronal population recruitment to response level in visual area MT: a computational model.

Adaptation is a form of short-term plasticity triggered by prolonged stimulus exposure, altering perceptual sensitivity to stimulus features through reduced neuronal firing rates. Our previous studies investigated adaptation to bistable stimuli, specifically inward-moving gratings perceived either as a plaid moving coherently downward or two gratings moving incoherently. Using functional magnetic resonance imaging (fMRI), we have consistently observed a stronger response to incoherent rather than coherent motion. Possible mechanisms include stronger adaptation to coherent motion, greater neural involvement for the representation of incoherent motion or both. Here, we employ a computational model of visual neurons with and without firing rate adaptation to test these two hypotheses. By simulating the mean activity of thirty-two columnar populations of visual area MT, we investigate the impact of adaptation on the blood-oxygen-level-dependent (BOLD) signal. Our results replicate experimental findings only when the model includes adaptation. The simulated response to incoherent motion is larger for a variety of stimulus parameters and adaptation regimes, suggesting that the reduced response to coherent stimuli is due to smaller neuronal population activation. The model also explains differential motion after-effect responses. The joint role of adaptation and differential neuronal recruitment in bistable perception sheds light on mechanisms underlying experimental data.